1. Field of the Invention
This invention relates to a solid state imaging apparatus in which a solid state imaging device chip and substrate are face-bonded with each other.
2. Description of the Related Art
Recently, there is extensively utilized an endoscope whereby organs within a body cavity can be observed by inserting an elongate insertable section into the body cavity and various therapeutic treatments can be made by using, as required, a treating instrument inserted through a treating instrument channel. There is also used an electronic endoscope provided with a solid state imaging apparatus in the tip part of an insertable section.
In the endoscope, it is desirable that the insertable section is made small in diameter to reduce the pain or the like of the patient and therefore, in the above mentioned electronic endoscope, it is desirable that the solid state imaging apparatus provided in the tip part of the insertable section is also made small.
FIG. 1 shows an example of a solid state imaging apparatus of the prior art. This solid state imaging appartus has a CCD chip 101 as an image sensor. This CCD chip 101 is made of such semiconductor as silicon and is fitted in a package 102 made of ceramics. The above mentioned chip 101 is fixed by being die-bonded with a silver solder 104 or the like on a coval plate electrode 103 on the package 102 to give a reference potential to the chip 101. The above mentioned coval plate electrode 103 is connected to a part of a lead frame 105 within the package 102 so that the reference potential may be given through this lead frame 105. A bonding pad 106 for inputting and outputting with the outside a driving signal required for the CCD chip 101 and an output signal from the CCD chip 101 is provided on the CCD chip 101. This bonding pad 106 is conducted to a bonding pad 108 on the package 102 through a bonding wire 107. The bonding pad 108 on the package 102 is conducted to the lead frame 105 within the package 102. This lead frame 105 projects out as a signal terminal. The above mentioned CCD chip 101 is sealed air-tight with a face plate 109 made mostly of glass so as to be protected from humidity and dust.
In the case of a color chip CCD or the like, a color filter array 110 is pasted on the imaging surface of the CCD chip 101. This color filter array 110 is made by forming a color filter of a pixel density on glass and is pasted directly on the CCD chip 101 with an optical bonding agent in one case or is fixed to the package 102 by utilizing the step difference of the package 102 the same as in the illustrated face plate 109 in the other case.
Here, by using FIG. 2, there shall be explained the dimensions required for the bonding between the CCD chip 101 and package 102.
For example, the size of the bonding pad 106 on the CCD chip 101 side is 100 .mu.m.times.100 .mu.m and its pitch is 150 to 200 .mu.m. The distance l between the bonding pads 106 and 108 conducted by the bonding wire 107 is 0.7 to 1.0 mm, will be required to be 1.0 mm in the case of bonding by using an automatic bonding machine and will be 0.7 mm in the case of manually bonding. The flexing height h of the bonding wire 107 is 0.4 to 0.6 mm.
Here, in case the dimensions of the solid state imaging apparatus including the package 102 are to be reduced to the extreme, the dimensions required for the above mentioned distance l and height h, respectively, in the plane direction and height direction of the CCD chip 101 will be main factors. So long as the electric connection depends on the bonding wire 107, the contraction limit dimensions will be controlled by the above mentioned required dimensions of l and h.
In the publication of Japanese Patent Application Laid Open No. 67863/1987 is disclosed a technique of making only a solid state imaging apparatus small in a packaging state by making the material of the package a molded resin. However, as described above, the required dimensions by the wire bonding are not avoidable.
Here, the structure of an electronic endoscope provided with a solid state imaging apparatus in the tip part of an insertable section shall be considered. In the electronic endoscope, as it is desired to make the insertable section as small as possible in the diameter, the electronic parts fitted in the tip part are kept to a required minimum. The electric formation in the tip part including these electronic parts is as shown, for example, in the publication of Japanese Patent Applicatin Laid Open No. 209836/1987 and U.S. Pat. No. 4,868,646. The formation shall be explained by using FIG. 3.
Respective cables for a power source voltage VDD, earthing GND and driving signal are connected to a CCD chip 101. The CCD chip 101 requires various bias voltages in addition to the power source voltage. If it is intended to reduce the number of the cables to make the electronic endoscope small in the diameter, as shown in FIG. 3, it will be desirable to generate various bias voltages from the above mentioned power source voltage VDD with an IC 111 for generating various bias voltages. Because these various bias voltages differ in optimum value depending on the respective CCD chips 101, if formed as described above, the optimum voltage will be able to be generated in the tip part of the insertable section of each electronic endoscope and each electronic endoscopce may feed only the common power source voltage VDD, providing interchangeability.
Also, in the electronic endoscope, as shown in FIG. 3, there are required at least a bypass condenser 112 for stabilizing the power source voltage VDD in the tip part and a cable driving buffer IC 113 for cable-transmitting a CCD output signal.
Their connection with each other is as shown in FIG. 4. That is to say, the three of the CCD chip 101, a substrate 114 on which the electronic parts in the tip part are mounted and a scope cable 115 electrically connecting this substrate 114 with a signal processing apparatus outside the endoscope are tandem connected.
Such formation of a solid state imaging apparatus in the tip part of an insertable section as is shown in FIG. 5 is disclosed in the publication of Japanese Patent Application Laid Open No. 141788/1990. The CCD as a solid state imaging device is an interline transferring system which is the current trend today. In the case of a frame transferring system, the number of lines of driving pulses is larger than in the line transferring system and, if all the lines necessary to feed the above mentioned various bias voltages are combined, the number of terminals will be ten and several terminals. The array of two rows of CCD outside lead terminals 117 extended out of a package 102 fitted to the CCD chip 101 as shown in FIG. 5 is general and ideal. Therefore, the structure of the tip part of the insertable section of the electronic endoscope in which, as shown in FIG. 5, two of a first connected substrate 121 and a second connected substrate 122 are prepared for connected substrates to be connected to the package 102, the respective connected substrates 121 and 122 are connected by soldering 123 to the respective rows of the lead terminals 117 of the package 102 and further cables 115 are connected respectively to the connected substrates 121.
However, even in this case, in order to make the solid state imaging apparatus including the substrate smaller, there are two problems. The first problem is the waste space of soldering and connecting the outside lead terminals 117 and the first and second connected substrates 121, and 122 and the bad influence from heat generated by soldering The second problem is that the first connected substrate 121 and second connected substrate 122 are respectively independent, and therefore can be connected only with the CCD outside lead terminal 117 and cable 115, and can not give and take electric signals between them.
The cable 115 transmitting such signal not through the IC as the driving signal in FIG. 3 is conducted with the CCD chip 101 through the second connected substrate 122 and the signal group requiring the current source voltage and respective IC's 111 and 113 is given to the first connected substrate. In order to further reduce the substrate part, such electronic parts as the IC's 111 and 113 and condenser 112 should be fitted more efficiently to the first connected substrate 121 and second connected substrate 122 but as described above no electric signal can be given and taken between both connected substrates, therefore the electronic parts will deflect to one connected substrate 121 and the connected substrate 121 mounting the electronic parts necessarily lengthens.
In case it is considered to contract the tip part of the insertable section of the electronic endoscope to be small, the defects of the prior art will be summarized as follows;
One defect is the restriction of the dimensions in the direction (horizontal direction) parallel to the imaging surface in the wire bonding part between the solid state imaging device chip and package and the restriction of the dimensions in the direction (height direction) vertical to the imaging surface. The second defect is the bad condition caused by shortening in the lengthwise direction the connected substrate mounting the electronic parts between the solid state imaging device chip and scope cable.
Further, Japanese Patent Application Laid Open No. 50544/1986 discloses a solid state imging device fitted to a package and a flexible printed substrate connected to the back surface of this package. In this prior example, the solid state imaging device is not directly connected to the substrate, but rather through the package and therefore, the package is large.
On the other hand, the publication of Japanese Patent Application Laid Open No. 221719/1985 discloses that a through hole provided in a flexible printed substrate is present in an electrode of a solid state imaging device chip and solder is poured into the through hole to cause the electrode of the solid state imaging device chip and the printed substrate to conduct with each other. This prior art example is more adapted than the above described prior art example to make the tip part small. However, as the printed substrate is pulled out in the direction parallel to the imaging surface, the size in this direction will become large.